U.S. patent application number 11/445179 was filed with the patent office on 2006-12-28 for optical recording medium, and recording and reproducing method and optical recording and reproducing apparatus of optical recording medium.
Invention is credited to Hiroyuki Iwasa, Masaru Shinkai, Michiaki Shinotsuka.
Application Number | 20060292493 11/445179 |
Document ID | / |
Family ID | 34656217 |
Filed Date | 2006-12-28 |
United States Patent
Application |
20060292493 |
Kind Code |
A1 |
Shinotsuka; Michiaki ; et
al. |
December 28, 2006 |
Optical recording medium, and recording and reproducing method and
optical recording and reproducing apparatus of optical recording
medium
Abstract
The present invention is aimed at providing a dual-layer
phase-change optical recording medium which allows a high-density
recording and a recording, where the optical recording medium has a
high recording sensitivity even to a low power light with a short
wavelength such as blue laser beam, does not cause noises such as
jitter, has superior overwrite performance and favorable
archivability, allows easier focusing and tracking and enables a
compatibility with a ROM. Therefore, it provides an optical
recording medium including a substrate and, on the substrate at
least a first recording composite layer, an intermediate layer, a
second recording composite layer and a cover substrate in this
order, wherein the groove depth of the cover substrate is such that
the magnitude of a push-pull signal of the first recording
composite layer is equal or greater with respect to a push-pull
signal of the second recording composite layer.
Inventors: |
Shinotsuka; Michiaki;
(Hiratsuka-shi, JP) ; Shinkai; Masaru;
(Yokohama-shi, JP) ; Iwasa; Hiroyuki;
(Yokohama-shi, JP) |
Correspondence
Address: |
Dickstein Shapiro Morin and Oshinky LLP
2101 L St NW
Washington
DC
20037
US
|
Family ID: |
34656217 |
Appl. No.: |
11/445179 |
Filed: |
June 2, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP04/17716 |
Nov 29, 2004 |
|
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11445179 |
Jun 2, 2006 |
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Current U.S.
Class: |
430/270.13 ;
369/275.2; 369/275.5; 428/64.5; 430/945; G9B/7.03; G9B/7.168 |
Current CPC
Class: |
G11B 7/0903 20130101;
G11B 7/24038 20130101; G11B 7/24079 20130101 |
Class at
Publication: |
430/270.13 ;
430/945; 369/275.5; 428/064.5; 369/275.2 |
International
Class: |
G11B 7/24 20060101
G11B007/24 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 3, 2003 |
JP |
2003-405229 |
Jul 9, 2004 |
JP |
2004-203662 |
Claims
1. An optical recording medium comprising: a substrate and, on the
substrate at least a first recording composite layer, an
intermediate layer, a second recording composite layer and a cover
substrate in this order, wherein the groove depth of the cover
substrate is such that the magnitude of a push-pull signal of the
first recording composite layer is equal or greater with respect to
a push-pull signal of the second recording composite layer.
2. The optical recording medium according to claim 1, wherein the
groove depth of the substrate (d.sub.1) and the groove depth of the
cover substrate (d.sub.2) satisfy the following equations with
regard to a light entering from the side of the cover substrate:
d.sub.1>d.sub.2; 0<d.sub.1.ltoreq.7.lamda./8n; and
0<d.sub.2.ltoreq.7.lamda./8n, wherein .lamda. represents a
recording and reproducing wavelength; n represents a refractive
index of the substrate; and the cases with .lamda./4n, .lamda./2n
and 3.lamda./4n are excluded.
3. The optical recording medium according to claim 1, wherein the
first recording composite layer comprises a reflective layer, a
first mterfacial layer, a first protective layer, a first recording
layer and a second protective layer in this order from the side of
the substrate.
4. The optical recording medium according to claim 3, wherein the
first recording layer comprises 60% by mole or greater of
Sb.sub.70Te.sub.30.
5. The optical recording medium according to claim 1, wherein the
second recording composite layer comprises a third protective
layer, a heat-releasing layer, a fourth protective layer, a second
recording layer and a fifth protective layer in this order from the
side of the intermediate layer.
6. The optical recording medium according to claim 5, wherein the
second recording layer comprises 40% by mole or greater of
Ge.sub.50Te.sub.50.
7. The optical recording medium according to claim 3, wherein the
first recording layer and the second recording layer comprise 0.1%
by atom to 5% by atom of an element selected from O, N and S.
8. The optical recording medium according to claim 3, wherein the
first recording layer and the second recording layer comprises an
element selected from V, Nb, Ta, Cr, Co, Pt and Zr.
9. The optical recording medium according to claim 5, wherein the
optical recording medium comprises a second interfacial layer
between the heat-releasing layer and the fourth protective
layer.
10. The optical recording medium according to claim 3, wherein the
first protective layer, the second protective layer, the fourth
protective layer and the fifth protective layer comprise a mixture
of ZnS and SiO.sub.2.
11. The optical recording medium according to claim 5, wherein the
third protective layer comprises any one selected from ITO and
IZO.
12. The optical recording medium according to claim 3, wherein at
least any one of the first interfacial layer and the second
interfacial layer comprises any one selected from a mixture of TiC
and TiO.sub.2, a mixture of ZrC and ZrO.sub.2, a mixture of SiC and
SiO.sub.2 and a mixture of CrC and CrO.sub.2.
13. The optical recording medium according to claim 3, wherein the
reflective layer and the heat releasing layer comprise any one of
Au and an Au alloy, Ag and an Ag alloy, and Cu and an Cu alloy.
14. A recording and reproducing method of an optical recording
medium comprising: irradiating a light beam; and performing at
least any one of recording and reproducing information, wherein the
optical recording medium comprises: a substrate and, on the
substrate at least a first recording composite layer, an
intermediate layer, a second recording composite layer and a cover
substrate in this order, wherein the groove depth of the cover
substrate is such that the magnitude of a push-pull signal of the
first recording composite layer is equal or greater with respect to
a push-pull signal of the second recording composite layer; the
light beam is irradiated from the side of the cover substrate; and
the recording and reproducing information are performed in each
recording composite layer of the optical recording medium.
15. An optical recording and reproducing apparatus comprising:
irradiating a laser beam from a light source to an optical
recording medium; and performing at least any one of recording and
reproducing information in the optical recording medium, wherein
the optical recording medium comprises: a substrate and, on the
substrate at least a first recording composite layer, an
intermediate layer, a second recording composite layer and a cover
substrate in this order, wherein the groove depth of the cover
substrate is such that the magnitude of a push-pull signal of the
first recording composite layer is equal or greater with respect to
a push-pull signal of the second recording composite layer.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation of Application PCT/JP20041017716,
filed on Nov. 29, 2004.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a single-sided dual-layer
optical recording medium for high-density recording having two
recording layers such as re-writable DVD's as well as a recording
and reproducing method and an optical recording and reproducing
apparatus of the optical recording medium, wherein the single-sided
dual-layer optical recording medium is hereinafter also referred to
as a phase-change optical information recording medium,
phase-change optical recording medium, optical information
recording medium or information recording medium.
[0004] 2. Description of the Related Art
[0005] In general, CD's and DVD's record binary signals and detect
tracking signals by using the reflectivity changes caused by the
light interference from the bottom of a concave pit and a mirror
surface. Recently, phase-change re-writable compact discs
(CD-Rewritable or CD-RW) are on the verge of being extensively
used, and various phase-change re-writable DVD's have been
proposed. Also, ISOM Technical Digest, '00 (2000), p. 210 proposes
a system high-density DVR with a capacity of 20 GB or greater by
shortening the recording and reproducing wavelength to 350 nm to
420 nm as well as increasing the numerical aperture while the
capacity of a DVD is 4.7 GB.
[0006] These phase-change re-writable CD's, DVD's and DVR's detect
signals of recorded information by using the changes in
reflectivity difference and phase difference caused by the
refractive index difference between an amorphous and crystal
states. A conventional phase-change optical recording medium has a
structure including a lower protective layer, a phase-change
recording layer, an upper protective layer and a reflective layer,
and the compatibility between CD's and DVD's may be maintained by
controlling the reflectivity difference and the phase difference
through multiple interferences among these composite layers.
Regarding the CD-RW with the reflectivity reduced to around 15% to
25%, the compatibilities of recording signals and groove signals
with CD's are ensured, and a reproducing is possible with a CD
drive with an amplification system which covers the low
reflectivity. Here, a recording in a phase-change optical recording
medium such as CD-RW and re-writable DVD include an overwrite (O/W)
recording in which a recording and an erasing are performed
simultaneously since the phase-change optical recording medium may
perform erasing and re-recording processes only by means of the
intensity modulation of one conversing light beam.
[0007] Also, a crystalline state, an amorphous state or a mixed
state thereof may be used for a phase-change information recording,
and multiple crystalline states may also be used. However, a
phase-change re-writable optical recording medium generally regards
a crystalline state as non-recording and erased states and performs
a recording by forming an amorphous mark.
[0008] As a material for the phase-change recording layer, a
chalcogen element, i.e. S, Se or a chalcogenide alloy including Te,
is often used. Examples thereof include a GeSbTe system having a
GeTe--Sb.sub.2Te.sub.3 pseudobinary alloy as a main component,
AgInSbTe system having an Sb.sub.0.7Te.sub.0.3 eutectic alloy as a
main component and a GeSbTe system. Among these, a
GeTe--Sb.sub.2Te.sub.3 pseudobinary alloy with excess Sb, in
particular having compositions near intermetallic compounds such as
Ge.sub.1Sb.sub.2Te.sub.4 and Ge.sub.2Sb.sub.2Te.sub.5, has mainly
been of practical use. Since these compositions are characterized
by crystallization with no phase separation, which is specific to
intermetallic compounds, and a high crystal growth rate, an
initialization is easy, and the recrystallization speed is high.
Therefore, pseudobinary alloy systems and intermetallic compounds
with neighboring compositions have been conventionally drawing
attention as a recording layer showing practical overwrite
performance (SPIE, vol. 2514 (1995), pp. 294 to 301).
[0009] In addition, Japanese Patent Application Laid-Open (JP-A)
No. 61-258787, 62-152786,01-63195 and 01-211249 report a
conventional recording layer composition which includes a GeSbTe
ternary composition or includes additive elements in addition to
the ternary composition as a base. However, materials having such
compositions are still in an early phase of development, and there
are many problems to be solved for the application to a
high-density optical recording medium such as re-writable DVR.
[0010] In particular, an optical system having a short wavelength
such as blue laser beam has a disadvantage of frequent noises in a
recording layer due to low beam power. Also, when a protective
layer between a substrate and a recording layer viewed from the
side of the incoming light is thickened, it is difficult to satisfy
simultaneously the overwrite performance and the preservation
property due to more variations in the thickness of the protective
layer and preservation difficulties, and this has been a challenge
in high-speed and high-density recording.
[0011] Regarding an optical recording medium which allows a
single-sided dual-layer optical recording, the reflectivity is low
at 5% to 7%, which is less than half of that of a conventional
optical recording medium. Considering a focus jump between two
layers, it is also a problem that focus and tracking are difficult
with small push-pull signals in jumping to the second recording
layer.
[0012] Regarding such single-sided dual-layer optical recording
medium, Japanese Patent Application Laid-Open (JP-A) No.
2003-141775 discloses a single-sided dual-layer optical disc
including two recording layers. Also, Japanese Patent (JP-B) No.
3216794 discloses an optical data recording medium including a
first writable data recording layer and a second writable data
recording layer. In addition, Japanese Patent Application Laid-Open
(JP-A) No. 2002-515623 discloses an optical information medium
including two phase-change recording layers which are sandwiched
between two dielectric layers.
[0013] These single-sided dual-layer optical recording media is
required to increase the transmittance of the recording layer on
the side of an incoming light, i.e. second recording composite
layer, for recording so that the light reaches the recording layer
opposite to the side of the incoming light, i.e. first recording
composite layer. However, the recording layer and furthermore a
heat-releasing layer should be sufficiently thick for satisfactory
recording, or there is a problem that recording and reproducing
properties such as jitter and modulation are insufficient.
[0014] Therefore, a dual-layer optical recording medium for
high-density recording which has a high recording sensitivity to a
red laser beam for a dual-layer DVD+RW or a low-power light having
a short wavelength such as a blue laser beam, does not cause noises
such as jitter, has superior overwrite performance and favorable
archivability, allows easier focusing and tracking and enables a
compatibility with a ROM has not yet been achieved, and a prompt
supply thereof is desired.
SUMMARY OF THE INVENTION
[0015] The present invention is aimed at resolving the conventional
problems and providing a single-sided dual-layer optical recording
medium which allows a high-density recording and a recording and
reproducing method of the optical recording medium, where the
optical recording medium, in response to the above requirements,
has a high recording sensitivity even to a low power light with a
short wavelength such as blue laser beam, does not cause noises
such as jitter, has superior overwrite performance and favorable
archivability, allows easier focusing and tracking and enables a
compatibility with a ROM.
[0016] The inventors of the present invention found out as a result
of keen examinations for resolving the problems that an addition of
groove conditions to an optical recording medium including a
substrate and, on the substrate, at least a first recording
composite layer, an intermediate layer and a second recording
composite layer disposed in this order allows easier focusing and
tracking and enables a compatibility with a ROM.
[0017] The present invention is based on the findings by the
inventors of the present invention, and the means solving the
problems are as follows. That is:
[0018] <1> An optical recording medium including a substrate
and, on the substrate at least a first recording composite layer,
an intermediate layer, a second recording composite layer and a
cover substrate in this order, wherein the groove depth of the
cover substrate is such that the magnitude of a push-pull signal of
the first recording composite layer is equal or greater with
respect to a push-pull signal of the second recording composite
layer. With the addition of groove conditions to the dual-layer
optical recording medium, the optical recording medium according to
<1> has a high recording sensitivity even to a low power
light with a short wavelength such as blue laser beam, does not
cause noises such as jitter, has superior overwrite performance and
favorable archivability, allows easier focusing and tracking and
enables a compatibility with a ROM.
[0019] <2> The optical recording medium according to
<1>, wherein the groove depth of the substrate (d.sub.1) and
the groove depth of the cover substrate (d.sub.2) satisfy the
following equations with regard to a light entering from the side
of the cover substrate: d.sub.1>d.sub.2;
0<d.sub.1.ltoreq.7.lamda./8n; and
0<d.sub.2.ltoreq.7.lamda./8n, wherein .lamda. represents a
recording and reproducing wavelength; n represents a refractive
index of the substrate; and the cases with .lamda./4n, .lamda./2n
and 3.lamda./4n are excluded.
[0020] <3> The optical recording medium according to
<1>, [0021] wherein the first recording composite layer
includes a reflective layer, a first interfacial layer, a first
protective layer, a first recording layer and a second protective
layer in this order from the side of the substrate.
[0022] <4> The optical recording medium according to
<3>, wherein the first recording layer includes 60% by mole
or greater of Sb.sub.70Te.sub.30.
[0023] <5> The optical recording medium according to
<1>, wherein the second recording composite layer includes a
third protective layer, a heat-releasing layer, a fourth protective
layer, a second recording layer and a fifth protective layer in
this order from the side of the intermediate layer.
[0024] <6> The optical recording medium according to
<5>, wherein the second recording layer includes 40% by mole
or greater of Ge.sub.50Te.sub.50.
[0025] <7> The optical recording medium according to
<3>, wherein the first recording layer and the second
recording layer include 0.1% by atom to 5% by atom of at least one
element selected from O, N and S.
[0026] <8> The optical recording medium according to
<3>, wherein the first recording layer and the second
recording layer include at least one element selected from V, Nb,
Ta, Cr, Co, Pt and Zr.
[0027] <9> The optical recording medium according to
<5>, wherein the optical recording medium includes a second
interfacial layer between the heat-releasing layer and the fourth
protective layer.
[0028] <10> The optical recording medium according to
<3>, wherein the first protective layer, the second
protective layer, the fourth protective layer and the fifth
protective layer include a mixture of ZnS and SiO.sub.2.
[0029] <11> The optical recording medium according to
<5>, wherein the third protective layer includes any one
selected from ITO and IZO.
[0030] <12> The optical recording medium according to
<3>, wherein at least any one of the first interfacial layer
and the second interfacial layer includes at least any one selected
from a mixture of TiC and TiO.sub.2, a mixture of ZrC and
ZrO.sub.2, a mixture of SiC and SiO.sub.2 and a mixture of CrC and
CrO.sub.2.
[0031] <13> The optical recording medium according to
<3>, wherein the reflective layer and the heat releasing
layer include any one of Au and an Au alloy, Ag and an Ag alloy,
and Cu and an Cu alloy.
[0032] <14> A recording and reproducing method of an optical
recording medium including: irradiating a light beam; and
performing at least any one of recording and reproducing
information, wherein the optical recording medium includes: a
substrate and, on the substrate at least a first recording
composite layer, an intermediate layer, a second recording
composite layer and a cover substrate in this order, and the groove
depth of the cover substrate is such that the magnitude of a
push-pull signal of the first recording composite layer is equal or
greater with respect to a push-pull signal of the second recording
composite layer; the light beam is irradiated from the side of the
cover substrate; and the recording and reproducing information are
performed in each recording composite layer of the optical
recording medium.
[0033] In the recording and reproducing method of an optical
recording medium of the present invention, at least a recording or
a reproducing of information is performed by irradiating a laser
beam to the optical recording medium of the present invention. As a
result, at least a recording or a reproducing of information may be
efficiently performed in a stable and reliable manner.
[0034] <15> An optical recording and reproducing apparatus
including: irradiating a laser beam from a light source to an
optical recording medium; and at least any one of recording and
reproducing information in the optical recording medium, the
optical recording medium comprises: a substrate and, on the
substrate at least a first recording composite layer, an
intermediate layer, a second recording composite layer and a cover
substrate in this order, and the groove depth of the cover
substrate is such that the magnitude of a push-pull signal of the
first recording composite layer is equal or greater with respect to
a push-pull signal of the second recording composite layer.
[0035] In an optical recording reproducing apparatus which
irradiates a laser beam from a light source to an optical recording
medium and performs at least any one of recording and reproducing
of information in the optical recording medium, an optical
recording and reproducing apparatus of the present invention uses
an optical recording medium of the present invention as the optical
recording medium. In the optical recording apparatus of the present
invention, at least a recording or a reproducing of information may
be efficiently performed in a stable and reliable manner.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] FIG. 1 is a cross-sectional diagram showing an example of
the layer composition of a dual-layer optical recording medium of
the present invention.
[0037] FIG. 2 is a cross-sectional diagram showing the layer
composition of a dual-layer optical recording medium of
Example.
[0038] FIG. 3 is a diagram showing the relation of the groove depth
of the substrate on the side of the incident light having a
wavelength of 405 nm and a numerical aperture of 0.65 with
push-pull signals as well as RF signals.
[0039] FIG. 4 is a diagram showing the relation of the groove depth
of the substrate on the opposite side of the incident light having
a wavelength of 405 nm and a numerical aperture of 0.65 with
push-pull signals as well as RF signals.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
(Optical Recording Medium)
[0040] An optical recording medium of the present invention
includes: a substrate; at least a first recording composite layer,
an intermediate layer, a second recording composite layer on the
substrate; and a cover substrate, in this order. It further
includes other layers according to requirements.
[0041] The groove depth of the cover substrate is such that the
magnitude of a push-pull signal of the first recording composite
layer is equivalent or greater with respect to a push-pull signal
of the second recording composite layer. This can improve the
focusing and tracking of in the two recording layers.
[0042] Regarding the `equivalence,` since the maximum measurement
error of a push-pull signal is around 3% and the push-pull signals
of the first recording composite layer and the second recording
composite layer are 97% when measured 3% less or 103% when measured
3% more, respectively, the maximum difference between them is 6%.
Therefore, they are considered equivalent when the difference of
measurement values falls within 6%.
[0043] More specifically, in a structure in which a light is
irradiated from the side of the cover substrate, when the relation
of the groove depth of the substrate (d.sub.1) and the groove depth
of the cover substrate (d.sub.2) is d.sub.1>d.sub.2, the groove
depth of the substrate which is on the opposite side of the
incident light is deeper, and the push-pull signal of the first
recording composite layer is greater than the push-pull signal of
the second recording composite layer. Since a reproducing signal
from the first recording composite layer is reduced by about 40% to
60% after it passes the second recording composite layer, the
push-pull signal of the first recording composite layer may be
approximated to the push-pull signal of the second recording
composite layer, and the focusing and tracking are stabilized.
Furthermore, a recorded RF signal may be brought to a reproducible
level. In this regard, however, the push-pull signal is zero when
the groove depth is .lamda./4n, .lamda./2n or 3.lamda./4n, where
.lamda. represents a recording and reproducing wavelength; n
represents the refractive index of the substrate; therefore these
groove depths are excluded. Also, the groove depth is greater than
zero and 7.lamda./8n or less. It is also possible to configure such
that d.sub.2>d.sub.1, but the layer having a larger push-pull
signal is arranged preferably on the opposite side since the
push-pull signal may be more easily obtained with larger groove
depth.
[0044] FIG. 3 shows the groove depth of the substrate on the side
of the incident light having a wavelength of 405 nm and a numerical
aperture of 0.65, push-pull signals and RF signals. FIG. 4 shows
the groove depth of the substrate on the opposite side of the
incident light having a wavelength of 405 nm and a numerical
aperture of 0.65, push-pull signals and RF signals.
[0045] Within the range of the groove depth shown in FIGS. 3 and 4,
the maximum value of the push-pull signal of the second recording
composite layer on the light incident side is 23, and the push-pull
signal of the first recording composite layer on the opposite of
the light incident side is 25. The values for the first recording
composite layer were slightly larger, and focusing and tracking
were stable in both the first and second recording composite
layers. Also, the RF signals for the first and second recording
composite layers were within a range where a recording and
reproducing was possible. Here, a larger RF signal is preferable
for reproducing. In FIGS. 3 and 4, the RF signals for the both
first and second recording composite layers are increased and the
magnitudes of the push-pull signals become almost equivalent when
the groove depths of the cover substrate and the substrate are 30
nm and 40 nm, respectively; therefore the properties improve.
[0046] The first recording composite layer in the optical recording
medium of the present invention includes at least a first
interfacial layer, a first protective layer, a first recording
layer and a second protective layer in this order from the
substrate, and it further includes other layers according to
requirements.
[0047] Also, the second recording composite layer includes at least
a third protective layer, a heat releasing layer, a fourth
protective layer, a second recording layer and a fifth protective
layer in this order from the intermediate layer, and it further
includes other layers according to requirement.
[0048] FIG. 1 schematically shows the cross-section of the layer
composition as an example of the optical recording medium of the
present invention. This optical recording medium including a first
recording composite layer 100 and a second recording composite
layer 200 has a structure including: a substrate 1, a reflective
layer 2, a first interfacial layer 14, a first protective layer 3,
a first recording layer 4, a second protective layer 5, an
intermediate layer 6, a third protective layer 7, a heat releasing
layer 8, a fourth protective layer 9, a second recording layer 10,
a fifth protective layer 11 and a cover substrate 13. Furthermore,
it may include a second interfacial layer (not shown) between the
heat releasing layer 8 and the fourth protective layer 9.
--Substrate--
[0049] As a material for the substrate 1, polycarbonate resins,
acrylic resins, transparent resins such as polyolefin resins or a
transparent glass may be used, for example. Among these,
polycarbonate resins are the most favorable material since it is
most extensively used for CD's and cost less.
[0050] A groove having a pitch of 0.8 .mu.m or less for guiding a
recording and reproducing light is usually allocated in the
substrate 1, and the groove does not have to be a geometric groove
having a rectangular or trapezoidal shape. For example, a groove
may be optically formed as a waveguide having a different
refractive index by means of ion implantation.
[0051] When an object lens with a high numerical aperture is used,
the cover substrate 13 has a sheet shape with a thickness of
preferably 0.3 mm or less, and more preferably 0.06 mm to 0.20 mm.
When the numerical aperture is around 0.6 to 0.65, a substrate
having a thickness of 0.6 mm is used
--First Recording Layer--
[0052] Preferable examples of a phase-change recording material
used for the first recording layer include an alloy having Sb and
Te as main components, and the content of Sb.sub.70Te.sub.30 is
preferably 60% by mole or greater, and more preferably 60% by mole
to 90% by mole. The content increased to 60% by mole or greater
abruptly improves the overwrite performance, and the content
exceeding 90% by mole may degrade the overwrite performance
again.
[0053] Among these, a material having Sb, Te and Ge as constituting
elements is preferable. To a recording layer including such
constituting elements, other elements may be added up to about 10%
by atom according to requirements. Also, the optical constants of
the first recording layer may be finely adjusted with an addition
of 0.1% by atom to 5% by atom of at least one element selected from
O, N and S to the first recording layer. However, an addition
exceeding 5% by atom is not preferable since it reduces the
crystallization speed and degrades the erase performance.
[0054] Also, an addition of 8% by atom or less of at least any one
element selected from V, Nb, Ta, Cr, Co, Pt and Zr is preferable in
order to improve the temporal stability without decreasing the
crystallization speed in overwriting, and the more preferable
content is 0.1% by atom to 5% by atom. The total content of these
elements and Ge with respect to SbTe is preferably 15% by atom or
less. The content exceeding 15% by atom induces the phase
separation of components other than Sb. The addition is
particularly effective when the content of Ge is 3% by atom to 5%
by atom.
--Second Recording Layer--
[0055] Preferable examples of a phase-change recording material
used for the second recording layer include an alloy having Ge and
Te as main components. The content of Ge.sub.50Te.sub.50 is
preferably 40% by mole or greater, and more preferably 40% by mole
to 90% by mole. The content increased to 40% by mole or greater
improves the overwrite performance even in a layer with high
transmittance. When it exceeds 90% by mole, the overwrite
performance may degrade.
[0056] Among these, a material consisting only of Ge and Te is
preferable. A second recording layer made up of such constituting
elements may be added with up to about 10% by atom of other
elements according to requirements. Also, the optical constants of
the second recording layer may be finely adjusted with an addition
of 0.1% by atom to 5% by atom of at least one element selected from
O, N and S to the first recording layer. However, an addition
exceeding 5% by atom is not preferable since it degrades the
recording and erase performance.
[0057] Also, an addition of 20% by atom or less of at least any one
element selected from V, Nb, Ta, Cr, Co, Pt and Zr is preferable in
order to improve the temporal stability without decreasing the
crystalization speed in overwriting, and the more preferable
content is 2% by atom to 15% by atom. The content exceeding 15% by
atom induces the phase separation of components of Ge atoms and Te
atoms.
[0058] Furthermore, as a material to be added to the first and
second recording layers, 5% by atom or less of at least one type of
element selected from Si, Sn and Pb for improvement of the temporal
stability and fine adjustment of the refractive index. The total
content of these elements and Ge is preferably 15% by atom or less.
Here, Si, Sn and Pb are elements having a four-coordinated network
similarly to Ge.
[0059] Also, an addition of 15% by atom or less of at least one
type of element selected from Al, Ga and In raises the
crystallization temperature as well as decreasing the jitter and
improving the recording sensitivity. However, it also causes
segregation, and the content is preferably 10% by atom or less.
[0060] Also, an addition of 8% by atom or less of Ag is effective
in terms of improving the recording sensitivity, and the effect is
particularly prominent when the content of Ge exceeds 5% by atom.
However, the content of Ag exceeding 8% by atom is not preferable
since it increases the jitter and impairs the stability of an
amorphous mark. The total content of Ag and Ge exceeding 15% by
atom is not also preferable since it tends to cause the
segregation. The content of Ag is most preferably 5% by atom or
less.
[0061] The first and second recording layers preferably have a
thickness of 5 nm to 100 nm. With the thickness less than 5 nm, a
sufficient contrast may not be easily obtained, and moreover the
crystallation speed tends to decrease, and an erase in a short
period of time may become difficult. On the other hand, with the
thickness exceeding 100 nm, an optical contrast may not be easily
obtained, and cracks tend to occur. Regarding the contrast, the
compatibility with reproducing-only discs such as DVD should be
maintained.
[0062] In a high-density recording where the shortest mark length
is 0.5 .mu.m or less, the first and second recording layers
preferably have a thickness of 5 nm to 25 nm. When the thickness is
less than 5 nm, the reflectivity is too low, and the effects of the
non-uniform composition and non-dense film at the initial stage of
film growth tend to appear. Therefore, it is not preferable. On the
other hand, when the thickness exceeds 25 nm, the increased heat
capacity degrades the recording sensitivity. Moreover, since the
crystal growth becomes three-dimensional, the edge of an amorphous
mark is distorted, and the jitter tends to increase. Furthermore,
the changes in the volume of the first and second recording layers
due to phase change become prominent, and the overwrite durability
degrades. Therefore, it is not preferable. The thickness is
preferably 20 nm or less in view of the jitter at the edge of a
mark and the overwrite durability.
[0063] The density of the first and second recording layers is
preferably 80% or greater of the bulk density, and more preferably
90% or greater. In order to increase the density in a sputtering
film-forming method, it is necessary by reducing the pressure of
the sputtering gas, e.g. noble gas such as Ar, in film formation or
by arranging the substrate close to the front of a target to
increase the amount of high-energy Ar irradiated to the recording
layers.
[0064] The high-energy Ar which reaches the substrate is either Ar
ions irradiated to the target for sputtering and partily bounced or
Ar ions in plasma accelerated by the sheath voltage in the whole
area of the substrate. Such irradiation effect of a high-energy
noble gas is called an `atomic peening effect.` In a generally-used
sputtering in an Ar gas, Ar is mixed into a sputtered film due to
`atomic peening effect.` The `atomic peening effect` may be
estimated based on this amount of Ar in the film. That is, a small
amount of Ar indicates that the high-energy Ar irradiation effect
is small, and a low-density film tends to be formed. On the other
hand, too much Ar indicates the irradiation of the high-energy Ar
is intense, and despite high density, the Ar entrained in the film
is released in repeated overwriting, which causes voids and
degrades the re-writing durability The appropriate amount of Ar in
a recording layer film is 0.1% by atom to 1.5% by atom.
Furthermore, the use of a high-frequency sputtering is preferable
to a direct-current sputtering since it reduces the amount of Ar in
a film and provides a high-density film.
[0065] The state of the first and second recording layers is
usually amorphous. Therefore, the whole area of each recording
layer should be crystallized after film formation to bring it to an
initialized state (non-recorded state). As an initialization
method, an initialzation by annealing in a solid phase is possible,
but an initiatliztion by melting and recrystallization that a
recording layer is once melted and then annealed in
re-solidification for crystallization is desirable. Each recording
layer above scarcely has any nucleus for crystal growth right after
the film formation, and the crystaization in a solid phase is
difficult. However, according to a melting and recrystallization,
by melting after the formation of a few crystal nuclei the
recrystallization proceeds at a high speed, driven by the crystal
growth.
[0066] Since the reflectivity of a crystal formed by melting and
recrystallization above is different from that of a crystal formed
by annealing in a solid phase, a mixture thereof causes noises.
Also, since the erased portion is a crystal formed by melting and
recrystallization in an actual overwrite recording, it is
preferable that the initialization is also performed by melting and
recrystallization.
[0067] In the initialization by melting and recrystallization, the
recording layer is melted preferably locally and in a short period
of time of about 1 msec or less. This is because the heat destroys
the layers and deforms the surface of a plastic substrate when the
melted area is too large or the melting or cooling time is too
long. In order to provide a thermal history appropriate for
initialization, it is desirable to irradiate a high-power
semiconductor laser beam having a wavelength of 600 nm to 1,000 nm
focused in an ellipsoid having a major axis of 100 .mu.m to 300
.mu.m and a minor axis of 1 .mu.m to 3 .mu.m and to scan at a
linear speed of 1 m/s to 10 m/s with the direction of the minor
axis as a scanning axis. The same focused beam having a shape close
to a circle is not preferable since the melted area is too large,
the layer tends to return to an amorphous state and the damages to
the layers in a laminated structure and substrates are severe.
[0068] The completion of the initialization by means of melting and
recrystallization may be confirmed as follows. That is, on an
optical recording medium after initialization, a recording light
focused in a spot diameter of less than about 1.5 .mu.m and having
a recording power sufficient for melting a recording layer is
irradiated at a constant velocity in a direct current manner. When
there is a guide groove, the light is irradiated while a tracking
servo or a focus servo is applied to a track composed of the groove
or intergroove.
[0069] Then, on the same track, an erase light having an erase
power of P.sub.e (P.sub.e.ltoreq.P.sub.w) is irradiated in a direct
current manner. When the reflectivity of the obtained erase state
is approximately equal to the reflectivity of the totally
non-recorded initial state, the initial state is confirmed as a
melted and recrystallized state. The reason is that the recording
layer which has once been melted by an irradiation of a recording
light and recrystallized by an irradiation of an erase light has
been through the a recrystallization process of melting by the
recording light and recrystallizing by the erase light and that the
recording layer is in a melted and recrystallized state. Here, that
the reflectivity at an initialized state, R.sub.ini, and the
reflectivity at a melted and recrystallized state, R.sub.cry, is
approximately equal means that the reflectivity difference thereof
defined by (R.sub.ini-R.sub.cry)/[(R.sub.ini-R.sub.cry)/2] is 0.2
or less, i.e. 20% or less. Usually, the reflectivity difference is
20% or greater solely with the solid state crystallization by
annealing.
--First, Second, Fourth and Fifth Protective Layers--
[0070] As shown in FIG. 1, the first recording layer is arranged
such that it is sandwiched between the first protective layer and
the second protective layer, and the second recording layer is
arranged such that it is sandwiched between the fourth protective
layer and the fifth protective layer.
[0071] These first, second, fourth and fifth protective layers
which sandwich the respective recording layers are described
below.
[0072] The first protective layer has a function of efficiently
releasing heat to the reflective layer. Also, the second protective
layer is effective mainly in preventing the high temperature in
recording from deforming the surface of the intermediate layer. The
fourth protective layer has fumctions of releasing heat to the heat
releasing layer and the third protective layer as well as
preventing the mutual diffusion between the second recording layer
and the heat releasing layer. The fifth protective layer is
effective in adjusting the reflectivity and preventing the high
temperature in recording from deforming the cover substrate.
[0073] Materials for the first, second, fourth and fifth protective
layers are determined in terms of refractive index, thermal
conductivity, chemical stability, mechanical strength and adhesion.
The materials preferably have low thermal conductivity, and the
rough indication is 1.times.10.sup.-3 pJ/(.mu.mNnsec). It is
difficult to measure directly the thermal conductivity of a
thin-film material having a low thermal conductivity. The rough
indication may be obtained from a thermal simulation and the
measurement results of the actual recording sensitivity as an
alternative to the direct measurement.
[0074] Examples of the materials having a low thermal conductivity
include composite dielectrics including heat-resistant compounds
which has 50% by mole to 90% by mole of at least any one selected
from ZnS, ZnO, TaS.sub.2 and rare-earth sulfides, is highly
transparent and has a melting point or a decomposition point of
1,000.degree. C. or greater. Examples of the rare-earth sulfides
include composite dielectrics including 60% by mole to 90% by mole
of a sulfide of a rare earth such as La, Ce, Nd and Y. Among these,
a material having 70% by mole to 90% by mole of ZnS, ZnO, TaS.sub.2
and rare-earth sulfides is particularly preferable.
[0075] Examples of the heat-resistant compound having a melting
point or decomposition point of 1,000.degree. C. or greater
includes oxides, nitrides or carbides of Mg, Ca, Sr, Y, La, Ce, Ho,
Er, Yb, Ti, Zr, Hf V, Nb, Ta, Zn, Al, Si, Ge and Pb; and fluorides
of Ca, Mg and Li.
[0076] The oxides, sulfides, nitrides, carbides and fluorides do
not necessarily have a stoichiometric composition. Alteration of
compositions or mlxing for the sake of controlling the refractive
index is also valid.
[0077] The most preferable material for the first, second, fourth
and fifth protective layers is a mixture of ZnS and SiO.sub.2 in
view of the above notes and the consistency with the materials for
the first and second recording layers. In view of reducing the
manufacturing cost, it is advantageous to use the same materials
for each protective layer.
[0078] The layer composition of the optical recording medium of the
present invention belongs to a type of layer composition called a
quench structure. The quench structure provides high erase ratio by
means of high-speed crystalalation while avoiding the problem of
recrystalization in a formation of an amorphous mark by employing a
layer composition which promotes the heat release and enhances the
cooling speed during the re-solidification of a recording
layer.
[0079] The film thickness of the first and fourth protective layers
significantly affects the durability in repeated overwriting, and
it is important particularly in preventing the degradation of the
jitter. The film thickness is usually 3 nm to 30 nm. When the film
thickness is less than 3 nm, the retardation effect of the thermal
conductivity in the protective layer portion is insufficient, and
the recording sensitivity significantly degrades. Therefore, it is
not preferable. When the film thickness exceeds 30 nm, a sufficient
flattening effect of the temperature distribution in the direction
of a mark width may not be obtained. Moreover, the protective
layers tend to deform asymmetrically due to the difference in the
thermal expansion on both sides of the protective layers. A
repetition thereof accumulates microscopic plastic deformation
within the protective layers and increases noises. Therefore, it is
not preferable.
[0080] The film thickness of the first and fourth protective layers
is preferably 15 nm to 25 nm when the wavelength of a recording
laser beam is 600 nm to 700 nm; it is preferably 3 nm to 20 nm, and
more preferably 3 nm to 15 nm, when the wavelength is 350 nm to 600
nm.
[0081] The film thickness of the second and fifth protective layers
is preferably 30 nm to 150 nm, and more preferably 40 nm to 130 nm
in terms of the overwrite performance. When the film thickness is
less than 30 nm, the protective layers are prone to destruction due
to deformation of the recording layers while melting, and the
overwrite performance degrades. When the film thickness exceeds 150
nm, the fluctuation of the reflectivity tends to increase, and a
uniform recording is difficult.
[0082] The jitter may be maintained at a low level in a
high-density recording with the shortest mark length of 0.3 .mu.m
or less when the phase-change recording material is used. Further
attention should be paid regarding the layer composition of the
quench structure when a laser diode having a short wavelength of,
for example, 410 nm or less is used to achieve a high-density
recording. Particularly in discussing the one-beam overwrite
performance of a small focused beam having a wavelength of 500 nm
or less and a numerical aperture of 0.55 or greater, a flattening
of the temperature distribution in the direction of a mark width is
important in order to obtain a high erase ration and a large erase
power margin. The tendency is synonymous for a DVR-compliant is
optical system which uses an optical system having a wavelength of
350 nm to 420 nm and a numerical aperture of around 0.85.
[0083] To provide the light transmittance as well as radiation
property and to increase the recording sensitivity, Au is used for
the heat releasing layer, the second interfacial layer is removed,
and the thickness of the heat releasing layer is 2 nm or greater
and less than 10 nm, then a design in which the sensitivities of
the two recording layers are tuned is possible.
[0084] In a high-density mark length modulation recording with an
optical system described above, it is important to use a material
having a low thermal conductivity is used for the first and fourth
protective layers and preferably to have the film thickness to be 3
nm to 20 nm. Thus, the first interracial layer disposed on the
first protective layer should have a high thermal conductivity.
This structure prevents the rapid escape of heat in a high-speed
recording and allows heat transfer to a reflective layer, and
therefore, a high-speed recording becomes possible.
[0085] A light which reaches the first recording composite layer is
a transmitted light which has transmitted the second recording
composite layer, and the amount of the incident light is less than
half of the amount of the incident light in the second recording
composite layer. Therefore, it is desirable to either increase the
incident light of the second recording composite layer or improve
the sensitivity of the first recording layer.
[0086] In the present invention, the recording sensitivity may be
improved by sandwiching the first recording layer with layers
having a low thermal conductivity in the first recording composite
layer with a small amount of incident light, and the recording
sensitivity may also be improved by reducing the film thickness of
the first protective layer to 3 nm to 20 nm for easier heat
absorption.
[0087] In the layer composition above, the radiation effect is
promoted by increasing the heat transfer coefficient of the first
protective layer or the fourth protective layer in view of only the
thermal conductivity. However, the thermal conductivity should be
kept low since excessive promotion of the radiation increases the
irradiation power required for recording and hence reduces the
recording sensitivity significantly.
[0088] The use of a thin-film protective layer having a low thermal
conductivity gives a temporal delay in the heat transfer from the
recording layer to the reflective layer and the heat releasing
layer at several nanoseconds to several tens of nanoseconds at the
starting point of the recording power irradiation and promotes the
radiation to the reflective layer and the heat releasing layer.
Therefore, the heat conducting property of the protective layer
keeps the reduction of the recording sensitivity to a minimum.
[0089] Because of the above reasons, the use of conventionally
known protective layer materials having SiO.sub.2, Ta.sub.2O.sub.5,
Al.sub.2O.sub.3, AlN and SiN as a main component by themselves is
not preferable because of their high thermal conductivity.
--Third Protective Layer--
[0090] Examples of the materials preferable for the third
protective layer include ITO (a mixed composition of
In.sub.2O.sub.3 and SnO) and IZO (a mixed composition of
In.sub.2O.sub.3 and ZnO), which can raise the light transmittance
to 70% or greater. These materials have a high thermal
conductivity, and the heat generated in recording in the second
recording layer is released through the heat releasing layer. This
provides an optimal quench condition for the recording layer formed
with a phase-change material having SbTe which requires rapid
quenching as a main component, and a small amorphous mark may be
formed.
[0091] A thicker third protective layer is more preferable in view
of radiation effect, but the thickness exceeding 200 nm increases
the stress and causes cracks. Also, the thickness less than 20 nm
provides insufficient radiation effect. Therefore, the third
protective layer has a thickness of preferably 20 nm to 200 nm, and
more preferably 30 nm to 160 nm.
--First and Second Interfacial Layers--
[0092] Regarding a phase-change optical recording medium which
satisfies the layer composition of the present invention and has a
layer composition equivalent to a phase-change optical recording
medium having a first interfacial layer and a second interfacial
layer with a thickness of 4 nm and composed of
(TiC).sub.80(TiO.sub.2).sub.20, i.e. the same composition as
Example 1, except that the phase-change optical recording medium
does not include any one of the first and second interfacial layer,
Table 1 shows comparative results of the recording sensitivity in
the first recording layer, i.e. the archivability in storing at a
temperature of 80.degree. C. and a relative humidity (RH) of
85%.
[0093] Here, a random signal was recorded under the following
recording and reproducing conditions: [0094] Wavelength of a
recording and reproducing light: 405 nm; [0095] Numerical aperture
of an object lens: 0.85; [0096] Recording linear velocity: 6.0 m/s;
[0097] Recording linear density: 0.160 .mu.m/bit; [0098] Recording
power at which the jitter was the smallest: 9.0 mW; [0099]
Reproducing power: 0.5 mW; and [0100] Recording pattern: 1 to 7
modulations.
[0101] Also, the jitter is .sigma./T.sub.w, i.e. the window width.
TABLE-US-00001 TABLE 1 Archivability (80.degree. C. and 85% RH)
With Without With Without First First Second Second Interfacial
Interfacial Interfacial Interfacial Layer Layer Layer Layer Initial
Jitter (%) 7.9 8.1 8.2 8.3 Jitter (%) after 300 hours 7.9 25.8 8.3
26.3
[0102] The results of Table 1 indicate that the archivability
degrades when the first interfacial layer or the second interfacial
layer are not included.
[0103] When any one of (TiC).sub.80(TiO.sub.2).sub.20,
(ZrC).sub.80(ZrO.sub.2).sub.20, (SiC).sub.80(SiO.sub.2).sub.20 and
(CrC).sub.80(CrO.sub.2).sub.20 is used as a material for the first
and second interfracial layers, little alteration due to oxidation
is observed even with the use of Ag and Al in the reflective layer
and the heat releasing layer since these materials are stable and
the amount of oxygen in the materials is small at 10% by mass or
less. The archival storage stability of an optical recording medium
in which the above materials were combined with a reflective layer
and a heat releasing layer composed of Ag was examined by
preserving the medium at a temperature of 80.degree. C. and a
relative humidity (RH) of 85% for 200 hours, and the jitter of a
recorded mark did not change, and favorable properties were
exhibited.
[0104] Heat may be easily released to the reflective layer by
thinly forming the first and second interfacial layers such that
the film thickness thereof is 2 nm to 15 nm, and preferably 3 nm to
10 nm. When the protective layers include S and the reflective
layer includes Ag, Ag is prone to sulfuration. Therefore, the film
thickness should be at least 2 nm to suppress the sulfration
reaction. On the other hand, when the layers are too thick, heat
tends to remain, and a small mark cannot be recorded. Therefore, it
is preferably 15 nm or less for the case of a blue wavelength.
[0105] However, as stated above, the radiation property of the
second recording composite layer is insufficient only with the
radiation property of the third protective layer. In a recording
layer composed of a phase-change material, an amorphous mark is
formed by means of the initial quenching, and the configuration in
which the third protective layer is combined with the heat
releasing layer for the sake of improving the radiation property
can improve the high-density recording property, overwrite
performance and preservation stability.
--Reflective Layer--
[0106] The use of a material with particularly high thermal
conductivity in the reflective layer can improve the erase ratio
and erase power margin. As a result of examination, it has been
found preferable that a layer composition in which the temperature
distribution in the direction of the film surface, i.e. in a
direction perpendicular to the recording beam scanning direction,
is also flattened to the best degree in addition to the temperature
distribution in the direction of the film thickness and the time
variation in order to bring out a favorable erase performance which
the recording layers of the present invention has in a wide range
of erase power. Therefore, in the present invention, it is
preferable to promote the radiation effect in a lateral direction
by using a thin reflective film having an extremely high thermal
conductivity and a thickness of 300 nm or less.
[0107] In addition, the thermal conductivity of a thin film is
generally small compared to the thermal conductivity in a bulk
condition. In particular, a thin film having a thickness of less
than 40 nm is not preferable since there are cases where its
thermal conductivity is smaller by one or more order of magnitude
due to the effect of an island structure in the initial stage of
the growth. Furthermore, the crystallization property and the
amount of impurities vary depending on film-forming conditions, and
attention must be paid since films having an identical composition
may have a different thermal conductivity.
[0108] Although the radiation by means of the reflective layer in
the first recording composite layer may be promoted by thickening
the reflective layer, the heat conduction in the direction of the
film thickness rather than the film surface of the first recording
layer becomes apparent with the thickness exceeding 300 nm, and the
improvement effect of the temperature distribution in the direction
of the film surface may not be obtained. Also, the heat capacity of
the reflective layer increases, and the increase in the cooling
time of not only the reflective layer but also the first recording
layer inhibits the formation of an amorphous mark. It is the most
preferable to arrange a thin reflective layer having a high thermal
conductivity and to promote selectively the radiation in a lateral
direction. A conventional quench structure focuses only on
one-dimensional radiation in the direction of the film thickness
and intends only the rapid radiation from the first recording layer
to the reflective layer, and it has not paid enough attention to
the flattening of this temperature distribution in the planar
direction.
[0109] Examples of a material for the reflective layer include: Au
and an Au alloy; Ag and an Ag alloy; Cu and a Cu alloy; and Al and
an Al alloy. The Ag alloy preferably includes 90% by atom or more
of Ag. Examples of the additive elements include Cu, Pt and Pd.
[0110] When Ag or an Ag alloy is used as the reflective layer, the
reflective layer preferably has a thickness of 30 nm to 200 nm.
When the thickness is less than 30 nm, the radiation effect is
insufficient. The thickness exceeding 200 nm does not contribute to
the improvement of the heat distribution in the horizontal
direction since heat is released more in the perpendicular
direction than in the horizontal direction, and an unnecessarily
thick film reduces the productivity. Also, the microscopic flatness
of the film surface degrades.
[0111] Examples of the Al alloy include alloys to which 0.2% by
atom to 2% by atom of at least one type of element selected from
Ta, Ti, Co, Cr, Si, Sc, Hf, Pd, Pt, Mg, Zr, Mo and Mn is added. The
volume resistivity increases in proportion to the concentration of
the additive elements, and the hillock resistance improves.
Therefore, the alloy may be used in view of durability, volume
resistivity and film deposition rate. When the content of the
additive element is less than 0.2% by atom, the hillock resistance
is often insufficient depending on the film-forming conditions. On
the other hand, when the content exceeds 2% by atom, it becomes
difficult to obtain the low resistivity. The additive element is
preferably Ta when the temporal stability is important.
[0112] Furthermore, Al--Cu alloys including 0.3% by atom to 5.0% by
atom of Cu are also preferable. In particular, when the protective
layer has a dual-layer structure in which a film having a mixed
composition of ZnS and SiO.sub.2 and a film of Ta.sub.2O.sub.5 are
laminated, an Al--Cu alloy including 0.5% by atom to 4.0% by atom
of Cu is desirable since it satisfies the corrosion resistance, the
adhesion and the high thermal conductivity in a balanced manner.
Also, an Al--Mg--Si alloy including 0.3% by atom to 0.8% by atom of
Si and 0.3% by atom to 1.2% by atom of Mg is also preferable.
[0113] When the Al alloy is used as the reflective layer, the film
thickness is preferably 150 nm to 300 nm. When the thickness is
less than 150 nm, the radiation effect is insufficient. As in the
case of the Ag alloy, the thickness exceeding 300 nm does not
contribute to the improvement of the heat distribution in the
horizontal dction since heat is released more in the perpendicular
direction than in the horizontal direction, and an unnecessarily
thick film reduces the productivity Also, the microscopic flatness
of the film surface degrades.
[0114] Regarding the Ag alloy or the Al alloy used for the
reflective layer, it has been confirmed that the volume resistivity
increases in proportion to the concentration of the additive
elements. On the other hand, the addition of impurities generally
reduces the crystal grain size and increases the electron
scattering at a grain boundary, and hence it reduces the thermal
conductivity. The adjustment of the amount of impurities to be
added is required in order to obtain the intrinsic high thermal
conductivity of the material by increasing the crystal grain
size.
[0115] In the second recording layer of the present invention, the
crystal growth in re-solidification near the crystallization
temperature (T.sub.m) is rate-controlling for the
recrystallization. A rapid quench structure is effective for steady
and clear formation of an amorphous mark and its edge by maximizing
the cooling speed near T.sub.m. Also, the high-speed erasure near
T.sub.m has been possible with the flattening of the temperature
distribution in the film surface dicection, and the rapid quench
structure ensures the erasure by means of recrystaization up to a
higher erase power. Therefore, the application of a so-called
`rapid quench structure in view of the retardation effect of the
heat conduction in the third protective layer` to the second
recording composite layer relating to the present invention enables
the favorable transition to an amorphous phase and the formation of
a recording mark even with a configuration having a translucent
phase-change material.
--Heat Releasing Layer--
[0116] In the present invention, a heat releasing layer is disposed
for such rapid quenching. Regarding the formation of the heat
releasing layer, it is necessary to resolve the non-uniformity by
reducing the deposition rate in the film formation relative to the
reflective layer. The film thickness is desirably 2 nm or greater
and less than 10 nm. When the film thickness is less than 2 nm, the
film is non-uniform even though the deposition rate is reduced.
Unless the thickness is less than 10 nm, the transmittance of the
second recording composite layer does not increase, and a light
does not reach the first recording layer. The transmittance of the
second recording composite layer is desirably 40% or greater.
[0117] Examples of a material which are preferable for the rapid
quench structure include: Au and an Au alloy; Ag and an Ag alloy;
and Cu and a Cu alloy.
[0118] Au has a reflectivity of about 37% with a thickness of 200
nm, which is relatively low compared to Ag, which has a
reflectivity of about 88% with a thickness of 200 nm. However, the
absorption of Au is equivalent to that of Ag. Therefore, the high
transmittance is ensured when the thickness is 2 nm or greater and
less than 10 nm, and it is preferable as a translucent layer of the
second recording composite layer.
[0119] Regarding Ag or an Ag alloy, it is synonymous to the
reflective layer, and the favorable film thickness is 30 nm to 200
nm for the same reasons.
[0120] When the Al alloy is used as the reflective layer, the film
thickness is preferably 150 nm to 300 nm. When the thickness is
less than 150 nm, the radiation effect is insufficient. As in the
case of the Al alloy, the thickness exceeding 300 nm does not
contribute to the improvement of the heat distribution in the
horizontal direction since heat is released more in the
perpendicular direction than in the horizontal direction. Also, the
heat capacity of the reflective heat releasing layer itself
increases, and the cooling speed of the recording layer decreases.
Moreover, the microscopic flatness of the film surface
degrades.
[0121] The use of Cu or a Cu alloy as a heat releasing layer is
preferable as a translucent layer of the second recording composite
layer, provided that the adjacent layers preferably includes
neither sulfur (S) nor oxygen (O), since a high transmittance for a
red wavelength is ensured with the thickness is 2 nm or greater and
less than 10 nm as well as Cu is a material having a higher thermal
conductivity among metals.
[0122] The reflective layer and the heat releasing layer are
usually formed with a sputtering method or a vapor deposition
method, and the total impurity content including the amount of
impurities of the target and the vapor deposited materials combined
with the moisture and the oxygen entrained during film deposition
should be maintained at 2% by atom or less. Therefore, the ultimate
vacuum of the process chamber is desirably 1.times.10.sup.-4 Pa.
Also, when the film formation takes place at an ultimate vacuum of
10.sup.-4 Pa or worse, it is desirable to prevent the impurities
from being entrained by increasing the deposition rate to 1 nm/s or
greater, and preferably 10 nm/s or greater. Alternatively, when 1%
by atom or greater of additive elements are included by design, it
is desirable to prevent the entrainment of additional impurities by
increasing the deposition rate to 10 nm/s or greater.
[0123] There are cases where the film-forming conditions affect the
crystal grain size independently of the content of impurities. For
example, an amorphous phase coexists among crystal grains in an
alloy film that about 2% of Ta is mixed with Al, and the ratio of
the crystal phase to the amorphous phase depends on the
film-forming conditions. Also, sputtering at a lower pressure
increases the ratio of the crystal portion, decreases the volume
resistance and increases the thermal conductivity.
[0124] The composition of impurities or crystallinity in a film
also depends on the preparation of the alloy target used for
sputtering and the sputtering gas such as Ar, Ne and Xe. Thus, the
volume resistance of a thin film cannot be determined solely by the
composition of metal materials. It is desirable to reduce the
amount of impurities as described above to achieve high thermal
conductivity. At the same time, there is a tendency that pure
metals such as Ag and Al are inferior in corrosion resistance and
hillock resistance, and it is necessary to determine the optimum
composition in view of the balance between the both.
[0125] It is also effective to have the reflective layer laminated
for further improvement of the thermal conductivity and
reliability. In this case, it is composed such that at least one
layer has a thickness of 50% or greater of the total thickness of
all the layers and includes the material having a high thermal
conductivity which practically contribute to the radiation effect
and that other layers contribute to the improvement in the
corrosion resistance, adhesion with the reflective layer and
hillock resistance.
[0126] For example, when Ag having the highest thermal conductivity
and the lowest volume resistance among metals is used for the
reflective layer and the protective layer adjacent to Ag includes
S, the reflective layer is prone to corrosion due to suiliration of
Ag and shows a tendency that the degradation in repeated
overwriting is rather quick. It also shows a tendency to cause
corrosion in a high temperature and humidity acceleration test
environment.
[0127] Thus, when Ag or an Ag alloy is used as a low volume
resistance material, it is also effective to allocate an Al alloy
layer having a thickness of 1 nm to 100 nm as an interfacial layer
with the adjacent protective layer. The same materials mentioned
for the reflective layer may be used as the Al alloy. The
interfacial layer having a thickness of less than 1 nm provides an
insufficient protective effect, and the layer having a thickness
exceeding 100 nm sacrifices the radiation effect. Also, when the
thickness is 5 nm or greater, the layer may be formed uniformly,
avoiding the island structure.
[0128] Furthermore, when an Ag-alloy heat releasing layer and an
Al-alloy interfacial layer are used, it is further preferable to
dispose an interfacial oxidized layer by oxidizing the surface of
the Al alloy by 1 nm or more in the thickness since the combination
of the Ag and Al interdiffuses relatively easily. The interfacial
oxidized layer having a thickness exceeding 5 nm, or especially
exceeding 10 nm, is not preferable since it becomes a thermal
resistance and sacrifices the primary function as a heat releasing
layer with extremely high radiation property.
[0129] In order to select a reflective layer and a heat releasing
layer having a high thermal conductivity and showing favorable
properties in the present invention, it is possible to estimate the
quality of the thermal conductivity by means of electric resistance
although it is possible to measure the thermal conductivity of each
layer directly. This is because a favorable linear relationship
holds between the thermal conductivity and electrical conductivity
in a material such as metallic film where electrons mainly govern
the heat or electric conduction.
[0130] A thin-film electric resistivity is expressed as a
resistance value normalized by the film thickness and the area of
the measured region. The volume resistance and the area resistance
may be measured with a common four-point probe method, which is
standardized by JIS N7194. This method provides reproducible data
far more easily compared to an actual measurement of the thin-film
thermal conductivity itself.
[0131] As a preferable property of the reflective layer and the
heat releasing layer, the volume resistance is preferably 20
n.OMEGA.m to 150 n.OMEGA.m, and more preferably 20 n.OMEGA.m to 100
n.OMEGA.m. It is practically difficult to reduce the volume
resistance less than 20 n.OMEGA.m in a thin-film state. Even though
the volume resistance exceeds 150 n.OMEGA.m, the area resistance
may be decreased by thickening the film, for example, over 300 nm.
However, a sufficient radiation effect could not be achieved only
by reducing the area resistance of such material with high
volumetric resistance. This is presumably because the heat capacity
per unit area increases in a thick film. In addition, such thick
film consumes time for film formation and increases the material
cost. Therefore, it is not preferable in terms of manufacturing
cost, and the microscopic flatness of the film surface degrades as
well.
[0132] It is effective to form the multilayered reflective layer
and heat releasing layer in order to obtain a desired area
resistance with a desired film thickness by combining a material
having a high volume resistance and a material having a low volume
resistance. The adjustment of the volume resistance by alloying can
simplfy a sputtering process due to the use of an alloy target, but
it can also be an increasing factor of the target production cost
and the material cost of the medium. Therefore, the desired volume
resistance may be effectively obtained by laminating a thin film of
pure Ag or pure Au and a thin film of the additive elements.
Although the initial apparatus cost increases, but there are cases
where the medium cost may be reduced when the number of layers is
up to three. Preferably, the reflective layer has a laminated
structure having multiple metal films and having a total thickness
of 40 nm to 300 nm, and one or more metallic thin-film layer having
a volume resistance of 20 n.OMEGA.m to 150 n.OMEGA.m makes up 50%
or greater of the total thickness.
[0133] A cover substrate preferably has a thickness of 0.3 mm or
less, and more preferably 0.06 mm to 0.20 mm when an object lens
with high numerical aperture is used in a configuration in which
the cover substrate is thinly disposed as shown in FIG. 1. A cover
substrate having a thickness of 0.6 mm is used when the numerical
aperture is 0.50 to 0.70.
[0134] Examples of the material for the cover substrate include
polycarbonate resins, acrylic resins, epoxy resins, polystyrene
resins, acrylonitrile styrene copolymers, polyethylene resins,
polypropylene resins, silicone resins, fluorinated resins, ABS
resins and urethane resins. Among these, polycarbonate resins and
acrylic resins are preferable in view of superior optical
properties and cost.
[0135] As a method for forming a thin cover substrate using a
transparent sheet composed of these materials, a lamination method
in which a transparent sheet is attached through an ultraviolet
curing resin or a transparent two-sided adhesive sheet. It is also
possible to form a thin cover substrate by applying and curing an
ultraviolet curing resin on the protective layer.
[0136] The resins may be used for the intermediate layer and an
adhesive layer, and ultraviolet curing resins are preferable in
terms of cost.
[0137] For a blue LD having a wavelength of 405 nm and a numerical
aperture of around 0.6 to 0.65, the intermediate layer has a
thickness of preferably 20 .mu.m to 50 .mu.m, and more preferably
30 .mu.m to 40 .mu.m, with which the interference of signals from
respective layers may be reduced.
[0138] According to the present invention, a phase-change optical
recording medium which allows a high density recording may be
provided, where the optical recording medium has a high recording
sensitivity even to a low power light with a short wavelength such
as blue laser, does not cause noises such as jitter, has superior
overwrite performance and favorable archivability, allows easier
focusing and tracking and enables a compatibility with a ROM.
(Method for Recording and Reproducing an Optical Recording
Medium)
[0139] A recording and reproducing method of an optical recording
medium of the present invention irradiates a light beam from the
side of the cover substrate and performs at least any one of a
recording and a reproducing of information in each information
layer of the dual-layer optical recording medium.
[0140] More specifically, a light for recording such as
semiconductor laser having, for example, an oscillating wavelength
of 350 nm to 700 nm is irradiated from the side of the cover
substrate through the objective lens while the optical recording
medium is rotated at a constant linear velocity or a constant
angular velocity. This irradiated light is absorbed by the first
and second recording layers, causing the local increase in the
temperature. This forms an amorphous mark, and information is
recorded, for example. The information recorded as above may be
reproduced by irradiating a laser beam from the side of the cover
substrate to the optical recording medium rotated at a constant
linear velocity and by detecting the reflected light.
(Optical Recording and Reproducing Apparatus)
[0141] In an optical recording reproducing apparatus, which
irradiates a laser beam from a light source to an optical recording
medium and performs at least any one of recording and reproducing
of information in the optical recording medium, an optical
recording and reproducing apparatus of the present invention uses
an optical recording medium of the present invention as the optical
recording medium.
[0142] The optical recording and reproducing apparatus is not
particularly restricted and can be appropriately selected according
to applications. For example, it includes: a laser source as a
light source of a semiconductor laser which emits a laser beam; a
condensing lens which condenses the laser beam emitted from the
laser source to an optical recording medium mounted on a spindle;
an optical element which guides the laser beam emitted from the
laser source to the condensing lens and a laser detector; and a
laser detector which detects a reflected light of the laser beam.
It further includes other units according to requirements.
[0143] The optical recording and reproducing apparatus performs a
recording on an optical recording medium by guiding a laser beam
emitted from the laser source to the condensing lens by means of
the optical element and by condensing and irradiating the laser
beam to the optical recording medium by means of the condensing
lens. At this point, the optical recording and reproducing
apparatus guides the reflected light of the laser beam to the laser
detector and controls the laser quantity of the laser source based
on the laser quantity detected by the laser detector.
[0144] The laser detector converts the detected quantity of the
laser beam to a voltage or a current and outputs as a detection
signal.
[0145] Examples of the other units include a controlling unit. The
controlling unit is not particularly restricted as long as it can
control the operation of the respective units, and it can be
appropriately selected according to applications. Examples thereof
include a sequencer and a computer for irradiating and scanning an
intensity-modulated laser beam.
[0146] The present invention will be illustrated in more detail
with reference to examples given below, but these are not to be
construed as limiting the present invention.
EXAMPLE 1
--Preparation of Optical Recording Medium--
[0147] An optical recording medium having a layer composition shown
in FIG. 2 was prepared by sequentially forming on a polycarbonate
resin substrate 21: a reflective layer 22
(Ag.sub.97Cu.sub.1Pt.sub.1Pd.sub.1); a first interfaciai layer 34
[(TiC).sub.80(TiO.sub.2)]; a first protective layer 23
(ZnSSiO.sub.2); a first recording layer 24
(Ag.sub.5In.sub.5Sb.sub.65Te.sub.25); a second protective layer 25
(ZnSSiO.sub.2); an intermediate layer 26 (a UV-curing resin, SD318,
manufactured by Mitsubishi Materials Corporation); a third
protective layer 27 (IZO); a heat releasing layer 28
(Ag.sub.97Cu.sub.1Pt.sub.1Pd.sub.1); a second interfacial layer 35
[(TiC).sub.80(TiO.sub.2).sub.20]; a fourth protective layer 29
(ZnSSiO.sub.2); a second recording layer 30
(Ge.sub.43Te.sub.43Sn.sub.12N.sub.2); a fifth protective layer 31
(ZnSSiO.sub.2); and a cover substrate 33 (polycarbonate resin).
[0148] The thickness of each layer is shown below. The intermediate
layer 26 was formed with a spin-coating method; the cover substrate
was laminated through a transparent adhesive sheet (polycarbonate
sheet having a thickness of 75 .mu.m, manufactured by Teijin
Limited); and other layers were formed with a sputtering method
while controlling their thicknesses.
[0149] The layer thicknesses were as follows: the substrate 21: 0.6
mm; the reflective layer 22: 100 nm; the first interfacial layer
34: 2 nm; the first protective layer 23: 10 nm; the first recording
layer 24: 14 nm; the second protective layer 25: 60 nm; the
intermediate layer 26: 35 .mu.m; the third protective layer 27: 30
nm; the heat releasing layer 28: 5 nm; the fourth protective layer
29: 8 nm; the second recording layer 30: 12 nm; the fifth
protective layer 31: 130 nm; and the cover substrate: 0.6 mm. Also,
the substrate had a groove depth d.sub.1 of 35 nm, and the cover
substrate had a groove depth d.sub.2 of 30 nm.
EXAMPLE 2
--Preparation of Optical Recording Medium--
[0150] An optical recording medium of Example 2 was prepared in the
same manner as Example 1 except that the materials for the first
interfacial layer and the third protective layer were changed to
(ZrC).sub.80(ZrO.sub.2).sub.20 and ITO, respectively, that the
interfacial layer was removed and that the heat releasing layer was
replaced by Au having a thickness of 5 nm.
EXAMPLE 3
--Preparation of Optical Recording Medium--
[0151] An optical recording medium of Example 3 was prepared in the
same manner as Example 1 except that the materials for the first
interfacial layer and the second interfacial layer were changed to
(SiC).sub.80(SiO.sub.2).sub.20 and (CrC).sub.80(CrO.sub.2).sub.20,
respectively and that the groove depths of the substrate and the
cover substrate were changed to d.sub.1=75 nm and d.sub.2=90 nm,
respectively.
EXAMPLE 4
--Preparation of Optical Recording Medium--
[0152] An optical recording medium of Example 4 was prepared in the
same manner as Example 1 except that the materials for the first
interfacial layer and the second interfacial layer were changed to
(SiC).sub.80(SiO.sub.2).sub.20 and that the groove depths of the
substrate and the cover substrate were changed to d.sub.1=160 nm
and d.sub.2=150 nm, respectively.
EXAMPLE 5
--Preparation of Optical Recording Medium--
[0153] An optical recording medium of Example 5 was prepared in the
same manner as Example 1 except that the groove depths of the
substrate and the cover substrate were changed to d.sub.1=230 nm
and d.sub.2=220 nm, respectively.
EXAMPLE 6
--Preparation of Optical Recording Medium--
[0154] An optical recording medium of Example 6 was prepared in the
same manner as Example 1 except that the first interfacial layer
was not formed.
EXAMPLE 7
--Preparation of Optical Recording Medium--
[0155] An optical recording medium of Example 7 was prepared in the
same manner as Example 1 except that the second interfacial layer
was not formed.
EXAMPLE 8
--Preparation of Optical Recording Medium--
[0156] An optical recording medium of Example 8 was prepared in the
same manner as Example 1 except that the groove depths of the
substrate and the cover substrate were changed to d.sub.1=100 nm
and d.sub.2=35 nm, respectively.
COMPARATIVE EXAMPLE 1
--Preparation of Optical Recording Medium--
[0157] An optical recording medium of Comparative Example 1 was
prepared in the same manner as Example 1 except that the first
interfacial layer was not formed and that the groove depths of the
substrate and the cover substrate were changed to d.sub.1=60 nm and
d.sub.2=50 nm, respectively.
COMPARATIVE EXAMPLE 2
--Preparation of Optical Recording Medium--
[0158] An optical recording medium of Comparative Example 1 was
prepared in the same manner as Example 1 except that the groove
depths of the substrate and the cover substrate were changed to
d.sub.1=100 nm and d.sub.2=40 nm, respectively.
REFERENCE EXAMPLE
--Preparation of Optical Recording Medium--
[0159] An optical recording medium of Reference Example 1 was
prepared in the same manner as Example 1 except that the third
protective layer and the first and second interfacial layers were
not formed.
[0160] Regarding each optical recording medium obtained in Examples
1 to 8, Comparative Examples 1 to 2 and Reference Example 1, Table
2 shows the groove depths of the first and second recording
composite layers and the ratio of a push-pull signal, i.e. the
magnitude of the signal of the first recording composite layer with
the magnitude of the signal of the second recording layer regarded
as unity.
[0161] Here, the wavelength of the optical system was 402 nm, and
the refractive index n of a polycarbonate resin is 1.53.
TABLE-US-00002 TABLE 2 First Recording Second Recording composite
layer composite layer d.sub.1 groove depth Push- d.sub.2 groove
depth Push- (nm) Pull (nm) Pull Example 1 35 1.2 30 1 Example 2 35
1.2 30 1 Example 3 75 4.4 90 1 Example 4 160 1.5 150 1 Example 5
230 1.3 220 1 Example 6 35 1.2 30 1 Example 7 35 1.2 30 1 Example 8
100 1.0 35 1 Comparative 60 0.25 50 1 Example 1 Reference Example 1
35 1.2 30 1 Comparative 100 0.8 40 1 Example 2
[0162] The results of Table 2 indicate the groove depth of the
first recording composite layer of Comparative Example 1 is 60 nm.
However, this value is close to 66 nm (.apprxeq..lamda./4n=402
nm/(4.times.1.53)), and the tracking is difficult due to the
reduced push-pull signal in the second recording composite
layer.
[0163] Also, the transmittance of the second recording composite
layer varies with or without recording in the second recording
layer, and the magnitude of the push-pull signal of the first
recording composite layer is not easily stabilized unless it is
equal to or greater than that of the second recording composite
layer.
[0164] The component of each layer in each optical recording medium
of Examples 1 to 8, Comparative Examples 1 to 2 and Reference
Example 1 is shown in Tables 3-1 and 3-2. TABLE-US-00003 TABLE 3-1
Reflective Layer First Interfacial First, Second, Fourth and First
Recording Intermediate Substrate 21 22 Layer 34 Fifth Protective
Layers(*) Layer 24 Layer 26 Example 1 Polycarbonate
Ag.sub.97Cu.sub.1Pt.sub.1Pd.sub.1 (TiC).sub.80(TiO.sub.2).sub.20
ZnSSiO.sub.2 Ag.sub.5In.sub.5Sb.sub.65Te.sub.25 UV Resin (SD318)
Example 2 Polycarbonate Ag.sub.97Cu.sub.1Pt.sub.1Pd.sub.1
(ZrC).sub.80(ZrO.sub.2).sub.20 ZnSSiO.sub.2
Ag.sub.5In.sub.5Sb.sub.65Te.sub.25 UV Resin Example 3 Polycarbonate
Ag.sub.97Cu.sub.1Pt.sub.1Pd.sub.1 (SiC).sub.80(SiO.sub.2).sub.20
ZnSSiO.sub.2 Ag.sub.5In.sub.5Sb.sub.65Te.sub.25 UV Resin Example 4
Polycarbonate Ag.sub.97Cu.sub.1Pt.sub.1Pd.sub.1
(SiC).sub.80(SiO.sub.2).sub.20 ZnSSiO.sub.2
Ag.sub.5In.sub.5Sb.sub.65Te.sub.25 UV Resin Example 5 Polycarbonate
Ag.sub.97Cu.sub.1Pt.sub.1Pd.sub.1 (TiC).sub.80(TiO.sub.2).sub.20
ZnSSiO.sub.2 Ag.sub.5In.sub.5Sb.sub.65Te.sub.25 UV Resin Example 6
Polycarbonate Ag.sub.97Cu.sub.1Pt.sub.1Pd.sub.1 None ZnSSiO.sub.2
Ag.sub.5In.sub.5Sb.sub.65Te.sub.25 UV Resin Example 7 Polycarbonate
Ag.sub.97Cu.sub.1Pt.sub.1Pd.sub.1 (TiC).sub.80(TiO.sub.2).sub.20
ZnSSiO.sub.2 Ag.sub.5In.sub.5Sb.sub.65Te.sub.25 UV Resin Example 8
Polycarbonate Ag.sub.97Cu.sub.1Pt.sub.1Pd.sub.1
(TiC).sub.80(TiO.sub.2).sub.20 ZnSSiO.sub.2
Ag.sub.5In.sub.5Sb.sub.65Te.sub.25 UV Resin Comparative Example 1
Polycarbonate Ag.sub.97Cu.sub.1Pt.sub.1Pd.sub.1 None ZnSSiO.sub.2
Ag.sub.5In.sub.5Sb.sub.65Te.sub.25 UV Resin Reference Example 1
Polycarbonate Ag.sub.97Cu.sub.1Pt.sub.1Pd.sub.1 None ZnSSiO.sub.2
Ag.sub.5In.sub.5Sb.sub.65Te.sub.25 UV Resin Comparative Example 2
Polycarbonate Ag.sub.97Cu.sub.1Pt.sub.1Pd.sub.1
(TiC).sub.80(TiO.sub.2).sub.20 ZnSSiO.sub.2
Ag.sub.5In.sub.5Sb.sub.65Te.sub.25 UV Resin
[0165] TABLE-US-00004 TABLE 3-2 Heat Releasing Layer Third
Protective Layer Second Recording Groove Depth Cover Substrate
Second Interfacial 28 27 Layer 30 (d.sub.1/d.sub.2) (nm) 33 Layer
35 Example 1 Ag.sub.97Cu.sub.1Pt.sub.1Pd.sub.1 IZO (In.sub.2O.sub.3
and ZnO) Ge.sub.43Te.sub.43Sn.sub.12N.sub.2 35/30 Polycarbonate
(TiC).sub.80(TiO.sub.2).sub.20 Example 2 Au IZO (In.sub.2O.sub.3
and ZnO) Ge.sub.43Te.sub.43Sn.sub.12N.sub.2 35/30 Polycarbonate
None Example 3 Ag.sub.97Cu.sub.1Pt.sub.1Pd.sub.1 IZO
Ge.sub.43Te.sub.43Sn.sub.12N.sub.2 75/90 Polycarbonate
(CrC).sub.80(CrO.sub.2).sub.20 Example 4
Ag.sub.97Cu.sub.1Pt.sub.1Pd.sub.1 IZO
Ge.sub.43Te.sub.43Sn.sub.12N.sub.2 160/150 Polycarbonate
(SiC).sub.80(SiO.sub.2).sub.20 Example 5
Ag.sub.97Cu.sub.1Pt.sub.1Pd.sub.1 IZO
Ge.sub.43Te.sub.43Sn.sub.12N.sub.2 230/220 Polycarbonate
(TiC).sub.80(TiO.sub.2).sub.20 Example 6
Ag.sub.97Cu.sub.1Pt.sub.1Pd.sub.1 IZO
Ge.sub.43Te.sub.43Sn.sub.12N.sub.2 35/30 Polycarbonate
(TiC).sub.80(TiO.sub.2).sub.20 Example 7
Ag.sub.97Cu.sub.1Pt.sub.1Pd.sub.1 IZO
Ge.sub.43Te.sub.43Sn.sub.12N.sub.2 35/30 Polycarbonate None Example
8 Ag.sub.97Cu.sub.1Pt.sub.1Pd.sub.1 IZO (In.sub.2O.sub.3 and ZnO)
Ge.sub.43Te.sub.43Sn.sub.12N.sub.2 100/35 Polycarbonate
(TiC).sub.80(TiO.sub.2).sub.20 Comparative Example 1
Ag.sub.97Cu.sub.1Pt.sub.1Pd.sub.1 IZO
Ge.sub.43Te.sub.43Sn.sub.12N.sub.2 50/60 Polycarbonate
(TiC).sub.80(TiO.sub.2).sub.20 Reference Example 1
Ag.sub.97Cu.sub.1Pt.sub.1Pd.sub.1 None
Ge.sub.43Te.sub.43Sn.sub.12N.sub.2 35/30 Polycarbonate None
Comparative Example 2 Ag.sub.97Cu.sub.1Pt.sub.1Pd.sub.1 IZO
(In.sub.2O.sub.3 and ZnO) Ge.sub.43Te.sub.43Sn.sub.12N.sub.2 100/40
Polycarbonate (TiC).sub.80(TiO.sub.2).sub.20 (*) The first
protective layer: 23; the second protective layer: 25; the fourth
protective layer: 29; and the fifth protective layer: 31.
<Evaluation>
[0166] A condensed light beam was irradiated with an optical system
having a wavelength of 402 nm and a numerical aperture of 0.65 to
each optical recording medium of Examples 1 to 8, Comparative
Example 1 to 2 and Reference Example 1 above, and with a linear
velocity of 6.0 m/s or 0.160 .mu.m/bit, the initial jitter, the
recording sensitivity (recording power or a power for the smallest
jitter), the archivability and overwrite performance were evaluated
based on the following criteria. The results are shown in Tables
4-1 and 4-2.
<Archivability Criterion>
[0167] The time (hour) required until the jitter was increased by
20% or greater during storage at a temperature of 80.degree. C. and
a relative humidity of 85%.
<Overwrite Performance Criterion>
[0168] The number of overwrites (times) until the jitter was
increased by 20% or greater due to overwriting.
<Recording Sensitivity (Recording Power) Criterion>
[0169] The power with which the jitter was the minimum.
TABLE-US-00005 TABLE 4-1 First Recording Composite Layer Recording
Initial Overwrite Trans- Sensitivity Jitter Archivability
Performance mittance Example (mW) (%) (H) (times) (%) Example 1 7.5
6.8 2,000 10,000 48 Example 2 8 7.1 1,500 10,000 49 Example 3 8.5
6.9 2,000 10,000 48 Example 4 8 7.3 2,000 20,000 50 Example 5 8.5
7.2 2,000 10,000 48 Example 6 8 7.1 2,000 10000 49 Example 7 8.5
7.2 2,000 10,000 48 Example 8 8.0 6.9 2,000 10,000 51 Comparative
9.5 7.2 150 1,000 34 Example 1 Reference 10 7.2 300 1,000 38
Example 1 Comparative 8.5 7.1 2,000 10,000 42 Example 2
[0170] TABLE-US-00006 TABLE 4-2 Second Recording Composite Layer
Recording Initial Overwrite Sensitivity Jitter Archivability
Performance (mW) (%) (H) (times) Example 1 9.5 6.8 2,000 10,000
Example 2 9.5 7.1 1,500 10,000 Example 3 10 6.9 2,000 10,000
Example 4 9.5 7.3 2,000 20,000 Example 5 10 7.2 2,000 10,000
Example 6 9.5 7.3 2,000 10,000 Example 7 10 7.2 2,000 10,000
Example 8 8.5 6.9 2,000 10,000 Comparative Example 1 * * * *
Reference Example 1 * * * * Comparative Example 2 10.5 9.1 2,000
10,000 * A recording could not be performed due to focus
failure.
[0171] The results in Tables 4-1 and 4-2 indicate that the optical
recording media of Examples 1 to 8 showed the superior recording
sensitivity, archivability and overwrite performance compared to
Comparative Example 1.
[0172] On the contrary, the optical recording medium of Comparative
Example 1 showed the extremely poor preservation property, i.e.
archivability, high recording power and unfavorable sensitivity. In
addition, the optical recording medium of Comparative Example 2 had
the inferior recording sensitivity and initial jitter.
INDUSTRIAL APPLICABILITY
[0173] An optical recording medium of the present invention may be
extensively used for, for example, CD-RW, DVD+RW, DVD-RW, DVD-RAM
and Blu-ray Disc system which uses a blue-purple laser beam.
* * * * *